A Brooklyn public-school principal viciously slashed in the face had been the target of harassing phone calls and vandalism going back two years, law-enforcement sources said.

Investigators looking into the attack on Wanda Rivera-Switalski are checking out former employees at her school – including people who may have been transferred at her request.

Rivera-Switalski was standing outside her home in South Ozone Park, Queens, Wednesday morning when a masked man drove up on a motorcycle, jumped off and cut her twice with a boxcutter before speeding away, authorities said.

The victim, who needed as many as 100 stitches to close the wounds, only got a partial look at her attacker because of the mask, authorities said.

Investigators are focusing on former employees at her school, PS 190 at 590 Sheffield Ave., because of the phone calls two years ago.